1989 Mercury Black Max 135 spits/sputters/skips under load

[camphosts]

Hi there! We have been reading the forums ever since we purchased our first boat (a 1989 Procraft 1780V) a few months ago, and have found lots of useful information. Thanks! We've been able to troubleshoot and solve several smaller issues (like replacing a broken throttle cable) by following solutions on this forum, but we have hit a roadblock. When we purchased the boat, it ran wonderfully, reaching a max speed of about 55 mph.

A few weeks ago, we let it sit for a few days without using it, which was a first since we bought the boat! When we went out on the lake, when we tried to come out of the hole, it would lift up and drop back down. At WOT, it won't even go 5 mph. It spits, sputters, and seems to miss. Occasionally, if we keep running it, it will finally pick up speed a little at a time, but still spits and sputters and never reaches anywhere near max speed. (May hit 25-30 mph sometimes) One time since then, we started it up, and it ran great, up to 45 mph. That was a rarity though. It runs great @ idle, starts up every time, purrs like a kitten... until you get to 2000 rpm. Squeezing the primer bulb when it starts to sputter does nothing.

We originally thought it was bad fuel (we always use Sta-bil and every other time or so get the ethanol free fuel from the marina). We siphoned out/ ran out all the fuel and filled up again. Same problem. We then replaced the fuel line from the fuel tank to the engine, including the primer bulb (hoses were old and cracked). We installed new spark plugs- which made it run worse, so we replaced the old spark plugs. We replaced the fuel filter, did the Dunks Decarb method with 3 cans of Seafoam over the course of several days, all to no avail.
We did pull off the fuel pump and noticed that the rubber piece (the diaphragm????) seems like it's stretched. We've been trying to find a diagram of the fuel pump, but can't find one for our year and HP. Anyone know where we might find one? Trying to find a manual to order.

This may or may not be related. We've had some random alarms going off, but they started well after the engine problems above. A few times, the overheat alarm has gone off as soon as we start the boat - ie no time to overheat. We disconnected overheat sensor and it made no change in the engine problems. Also, this boat still has the VRO. We've read pros and cons to this and haven't decided which route to take. The oil alarm started going off occasionally well after the engine problems started. We checked the upper oil reservoir tank and it was low, so we filled it up with oil. The alarm stopped. We then decided to add oil to the gas in case the VRO has malfunctioned, assuming better safe than sorry. The oil alarm has gone off a couple times since then. Each time the tank was a little bit low, so we refilled and it stopped. I'm not sure why the tank is not refilling properly. I've read the possibility of the engine being stuck in limp/slow/get home mode, but it seems like it would not ever have gotten up to 25 or 45.

I (wife) read all the problems/ solutions on here and give him suggestions, which are mostly Greek to me!

Hubby can fix ANYTHING- he just needs to know what to fix!
I've read the BOAT acronym and am amazed how true that is! We'd love to be able to fix, rather than taking it to a mechanic. Any suggestions on what's wrong or what else we can try? Advice would be greatly appreciated! TIA

 

[sam am I]

Hmmmmmm, well it sounds like you've (wife) covered the fuel side of things fairly thoroughly and gave/wrote a very nice detail of whats going on thus far.

The diaphragms will tend to deform a tad over time, that's normal as long as its not ripped/leaking and seals properly, you're okay there. But, if you're inclined to rebuilding it, find your serial number on the engine and go here for a fuel pump rebuild kit...Guessing you're a 18-7817........

http://www.iboats.com/Mercury-Fuel-P...view_id.271585

Sierra ^^^ is OKAY, but for OEM go to

http://www.XXXXX/parts/detail/merc/M-42990A 3.html

where "XXXXX" = "boats . net" (remove spaces) to get the a mercury part number 42990A 3 fuel pump rebuild kit, bit higher quality IMO. Again guessing serial number, double check before ordering.

Next,

I'd do a quick compression/leak down test of the cylinders, then if that's okay'ish, it pretty much must be spark........

Sometimes wires will break(not seen by the eye per-se) down, can be arcing to the block and such under a load, and can be generally flaky.........so maybe in order of ease, do a quick wire check/replace, then I suppose you should/could pop in a compression test next.

Other than that, the power paks would be my next stop....i.e., check for good spark strength(gap jumping) and color of arc gig. w/o a nice strong spark, it'll idle good, but under load, she'll run poor.........

If I missed something, there's many good folks here that live, eat and breathe these things and'll chime in......we'll get ya going again!!

 

[Dukedog]

On tha oil thing. Tha main tank (in tha boat) is pressurized by tha motor. No pressure, no oil movement to motor tank. Check main tank cap and gasket for cracks and being tight. Right below tha starter there's one way check valve fitting with line going to tha boat tank. More than likely that fitting is bad. If your gonna keep tha oiler just replace that fitting if tha cap and gasket prove ta be good. Fitting part number is 43278. Forgot, check motor tank cap also.........

Tha terrible runnin' part can be several things. A fuel pump kit is never a bad thing. From what your describing I'd look at carburetor kits for fuel delivery problems AFTER determining its not an electrics problem. ie: trigger, stator, switch boxes etc. That motor should have NGK BU8H plugs period. No need ta get fancy just 'cause someone says this or that is better. If it doesn't run with those, it won't run right with anything.........

If ya want, I can get ya a link to OEM manual. Its for a little later motor but carb motor 'lectric's will be 'bout identical........

Oh yeah, check all tha motor wiring like Sam says!

 

[sam am I]

Duke,


She had mentioned that....

until you get to 2000 rpm. Squeezing the primer bulb when it starts to sputter does nothing.

At that age of motor, no doubt in my mind you're spot on that she needs carb and fuel pump kits, I'd be on it right now in fact......At least, to eliminate all possibilities anyway.

But, do you think when it "spits/sputters/skips under load", that squeezing the bulb would have eliminated the pump and carb's (fuel delivery) as her current issue?

In the carb, maybe her jets are restricting down w crap build up ya think'n?


OP(wife), Duke is right about kits, especially if your motor hasn't seen them......

If you do put in a carb kit and it has(most do) new float seats and valves, make extra extra sure the float level is adjusted to the spec height. It will be (99% sure) off with new parts and require adjustment.

 

[Dukedog]

Squeezing the primer bulb will usually just show something with fuel pump or floats. Not necessarily other carb problems. No change is a good thing...Another little fuel delivery test is enrichner circuit....Push it, motor loads and/or wants ta die fuel delivery should be good. Motor increases rpm, not so good. Probably got a carb deal. These arn't "cast in stone" ideas....jmo

99% of tha time tha WH series carburetor doesn't need needle n seat. Just a good cleanin' n NEW gaskets, floats tweaked.......unless they are really old like some of US!.

 

[camphosts]

Sam and Duke, thanks so much for your detailed responses. That definitely gives us some more ideas to try tomorrow! Duke, I'd definitely like a link to that manual. We did push the choke/enricher yesterday while trying a few more things, and it started to choke down/wanted to die. So that's a good thing, leading us away from fuel issues... I think. Thank you again! Will fill in more tomorrow after we try some things.

 

[camphosts]

Ok, tried the spark test. Referring to the left/non-driver's side, the top cylinder has great spark. The bottom and middle have minimal to no spark (repeated test). The right/ driver's side top has great spark again, bottom and middle have good spark. What does this mean?

 

[snowbrd84]

I dealt with a basically identical situation for the last two months. Read 100s of forum posts, tried everything under the sun, and here is what ended up being the problem.

Fuel, or lack there of it. First, my tank vent had a bunch of crap in the screen, it let just enough air through at idle and low speed that it would run, but when I gave it full throttle, it wouldnt give any more and just bogged out, but if I kept trying sometimes it would all of a sudden take off and would run fine at wot until i slowed back down. Made it look like it was a stator/carb/fuel pump issue, but in the end they were not the problem. I pulled the vent line off the tank and tried to blow through it and got a lot of resistance. I installed a new tank vent ($14) and actually installed it a little higher to keep it from getting dunked at take off.

After fixing the tank vent, I put it in the water and it fired right up and ran a lot smoother than before. I then went to head out and after about 100 yards, it died. Ran out of fuel, I went back and pumped the bulb but it wouldnt pump up. I have had the primer bulb located between the fuel/water separator and the engine since i installed it last year because thats how I was told to do it. Turns out, the fuel/water separator was not filling all the way, I then moved the bulb to be between the tank and the fuel/water separator so that it is pumping into the fuel/water separator and I noticed an immediate difference in the way it pumped and primed up. It got so hard I couldnt squeeze the bulb...

Fired right back up, and ran perfect all day, wot hole shot and it absolutely flies... Did not bogg out once. Everyone kept INSISTING that it was carbs or stator. Thats the only thing it could be... Well it wasnt.. I couldn't believe how simple the problem ended up being...

 

[Dukedog]

Ok, tried the spark test. Referring to the left/non-driver's side, the top cylinder has great spark. The bottom and middle have minimal to no spark (repeated test). The right/ driver's side top has great spark again, bottom and middle have good spark. What does this mean?

Sounds like switch box. Without havin' tha right stuff for testi' you can do this. Swap tha wires from box at tha coils. ie: firing coil with non firing coil. If tha problem follows box is bad. Change both boxes.....

SNOWBIRD, just one question. Who in tha "outboard marine world" told ya hook it up that way?

 

[sam am I]

Ok, tried the spark test. Referring to the left/non-driver's side, the top cylinder has great spark. The bottom and middle have minimal to no spark (repeated test). The right/ driver's side top has great spark again, bottom and middle have good spark. What does this mean?

Cool..........This is good news, perhaps not cheap news, but good/progressive news none the less!!

Sounds like switch box. Without havin' tha right stuff for testi' you can do this. Swap tha wires from box at tha coils. ie: firing coil with non firing coil. If tha problem follows box is bad. Change both boxes.....

^^^^ concur, either the problem (lack of proper spark) will follow the box or stay depending.......let us know.

Snippets from merc manual that relates well here +/- 5% (i.e., you might not have tilt switch etc., which is obviously beside main points made here) below to perhaps provide additional direction/reference....

 

[camphosts]

Snowbird, thanks for sharing. I'm thinking that can't be the case because we've ran it from a separate fuel tank with the same problem. (?) Of course, we're never lucky enough for a cheap fix! Glad you were!
We tested the spark plug wires, thinking that since there was no spark in those cylinders, the wires were bad. Well, the top 2 wires were fine, everything else was bad. So we're thinking this is it... NOPE! Replaced all spark plug wires, same problem. So maybe something caused those specific wires to burn up??? Visually everything else looks ok... Now I'm really confused... Guess we will try the switch box switching next, unless this means we should try something else.
Sam, those snippets didn't come through. I get a broken picture image.
Thanks again for all the replies!

 

[sam am I]

So maybe something caused those specific wires to burn up???

That depends on how they "burn't up" I suppose, if it wasn't like they were fire roasted then age, norm heat, cracking then the insulation/dielectric strength breaking down then on to arcing and the like can just make them go south over time.

Guess we will try the switch box switching next, unless this means we should try something else.

Yes and no, not that I can think of..... step at a time, switch boxes and coils are pretty much the next step w what has been identified/fixed and where we're at now.

Sam, those snippets didn't come through. I get a broken picture image.

Try this........

 

[camphosts]

Just wondering, could the rev limiter be engaging, or could it be stuck in "slow" mode somehow with the alarms that were going off?

 

[paddlers]

Hi, haven't read all the post but I've just had a similar problem with my Mariner 135 V6 early 90's. Turned out to be a magnet in the flywheel had cracked & come loose. Fairly common problem seemingly on these !!
I'm in the UK but picked up a proper Mercury flywheel puller £35, secondhand flywheel £50 job done. If you rotate the flywheel slowly and check the position of the magnets without removing it you may find out if you have a problem there!

 

[camphosts]

after 2 weeks, the mechanic says it needs a new stator. something about the high end on the stator has gone out. It makes sense I guess that the top two cylinders fire and the bottom ones don't. his estimate is $500 to replace. two questions... one, does this sound likely? two, how difficult is this to do myself? it looks fairly simple from what I've read, and I see stators on eBay for under $200. thanks in advance for any advice!

 

[snowbrd84]

A CDI stator will cost you $160 on eBay, I just use a cheapo steering wheel puller from HF ($13) to remove the flywheel. You could buy an actual flywheel puller for the Merc for pretty cheap too, under $50. If you have an impact wrench, it works GREAT for removing the flywheel bolt, dont even have to hold the flywheel. If you are doing it with a regular breaker bar by hand, its a PITA holding the flywheel in place. Its maybe an hours worth of work to remove and replace, including hooking up the wires. $500 is ALOT of money to replace a stator in my opinion.

 

[paddlers]

Careful with using anything other than the Mercury puller, the legged ones can damage the flywheel. I bought the puller, gave it a squirt of WD40 and it popped straight off with no issues. Needed some big sockets/spanners but fortunately was able to borrow them from a friend who has tractors. Replacing the stator looks straightforward. Just be sure it's not the magnets before you buy a stator, two of mine were cracked badly and it's a common failure. You can buy them in the USA for @$25 each including epoxy!

 

[Dukedog]

A bad hi side stator usually doesn't cause miss fires and/or "skippimg" as some describe. It usually runs smooth if all else is good with tha motor till it makes transition from low ta hi side. At that point it will only limit rpm max. Motor still runs smooth, just won't turn up. Did your guy actually dva test it?

Now tell us again about which plugs are NOT firing. They are numbered in this way. 1, 3, 5 are top ta bottom on starboard side. 2, 4, 6 top ta bottom on port side....It is very possible you could have 2 problems. Stator and switch box.....